Rotate type Dual Volume Control B50K (7-Pin)

Hello!

Can anyone tell me about the function of the 7th Pin of Volume Control. What does it mean?

I understand about 3-leg rotate type volume control (Mono) and 6-leg rotate type volume control (Stereo) application, but I do find volume controls of Japan/Singapore/Malayasian origin, which has 7th leg situated back to the single line 6-legged vol. controls. I found the volument control of (B50K) like this.
7
o
o o o o o o
1 2 3 4 5 6

Can anyone clarify...pls do not hesitate or mind for my poor english. If not understood, i will try to convince otherwise.

Please help!!!

regards,
shamim-india.
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Extra ground? Physical support? No idea.

Use your meter on ohms and measure what connects to where!.